1. Field of the Invention
The present invention relates to a method of manufacturing a superconducting quantum interference magnetic type fluxmeter, more specifically, a superconducting quantum interference magnetic type fluxmeter that employs a high-temperature superconductor thin film.
2. Description of the Related Art
The superconducting quantum interference device (to be called xe2x80x9cSQUIDxe2x80x9d hereinafter) type magnetic fluxmeter is a magnetic sensor having such a high sensitivity that a magnetic field of 1/5,000 or less of the terrestrial magnetism can be detected. The sensor utilizes the quantization phenomenon of the superconductor, and has a sensitivity higher by 3 figures or more than that of the conventional magnetic sensor. In particular, after the development of the SQUID magnetic fluxmeter using a high-temperature superconductor thin film, it has become possible to operate the sensor at a temperature of liquid nitrogen (77.3K), and therefore the field of the application is becoming wider.
The SQUID magnetic fluxmeter is a device in which junctions formed by finely processing superconducting thin film are connected to each other in parallel as shown in FIG. 1. When a bias current is allowed to flow to the SQUID magnetic fluxmeter, the voltage generated at both ends of the SQUID magnetic fluxmeter is zero since the superconducting state is maintained until the bias current becomes the critical value (Ic) as shown in FIG. 2. When the current exceeds the critical value, the SQUID magnetic fluxmeter changes its state to the normal conducting state, and thus a voltage is generated.
On the other hand, when a magnetic field is applied to the SQUID magnetic fluxmeter and a magnetic flux is put into a loop formed by the junctions connected to each other in parallel, the critical current value is lowered.
Incidentally, as shown in FIG. 3, if the bias current is fixed to the value close to the critical current and a magnetic field is applied from outside, the voltage generated at both ends of the SQUID magnetic fluxmeter changes. The strength of the magnetic field can be measured by detecting the change in the voltage.
However, such a SQUID magnetic fluxmeter that employs a conventional high-temperature superconductor thin film entails a drawback in which the manufacture of its pick-up coil is very difficult. More specifically, it is difficult to mold and process the high-temperature superconducting material, and it is not possible to finish it into the shape of a co-axial pickup coil. Therefore, a flat planar-type pickup coil is conventionally manufactured in the form of an integral body with a SQUID element, which is a thin film device.
In short, the co-axial type pickup coil made from a high-temperature superconducting material has never been manufactured.
As described above, the pickup coil of a conventional SQUID magnetic fluxmeter that employs a high-temperature superconducting material is of a planar type, which is, in actual measurement of magnetism, not sensitive for the magnetic gradient in a vertical direction to the SQUID element itself.
The present invention has been achieved under the above-described circumstances, and the object of the invention is to provide a method of manufacturing a superconducting quantum interference type magnetic fluxmeter equipped with a coaxial type pickup coil that has a high sensitivity to the magnetic gradient in a vertical direction to the SQUID element.
In order to solve the above-described drawbacks of the prior art, there is provided, according to the present invention, a method of manufacturing a superconducting quantum interference type magnetic fluxmeter characterized by comprising: forming a conductive pattern on an outer surface of a first cylindrical ceramic substrate; electrophoretically depositing high-temperature superconducting fine particles and/or high-temperature superconducting precursor fine particles on the conductive pattern; and subjecting the first cylindrical ceramic substrate to a heat treatment to sinter the fine particles, thereby forming an input coil and a pickup coil integrated with the input coil.
It is possible that the method of manufacturing a superconducting quantum interference type magnetic fluxmeter, according to the present invention, characterized by further comprising: forming a conductive layer on an inner surface of an upper section of the first cylindrical ceramic substrate, electrophoretically depositing high-temperature superconducting fine particles and/or high-temperature superconducting precursor fine particles on the conductive layer, and subjecting the first cylindrical ceramic substrate to a heat treatment to sinter the fine particles, thereby forming a first magnetic shield layer on the inner surface of the upper section of the first cylindrical ceramic substrate.
It is further possible that the method of manufacturing a superconducting quantum interference type magnetic fluxmeter, according to the present invention, characterized by further comprising: placing the pickup coil such that a distal end portion thereof is inserted within a lower end portion of a magnetic shield tube having a second high-temperature superconductor shield layer on an outer surface thereof; and inserting a high-temperature superconducting quantum interference type element from an upper end portion of the magnetic shield tube, thereby magnetically coupling the input coil and the high-temperature superconducting quantum interference type element.
In this case, the magnetic shield tube can be obtained by forming a conductive layer on an outer surface of a second cylindrical ceramic substrate having an inner diameter larger than an outer diameter of the pickup coil, electrophoretically depositing high-temperature superconducting fine particles and/or high-temperature superconducting precursor fine particles on the conductive layer, and subjecting the second cylindrical ceramic substrate to a heat treatment to sinter the fine particles, thereby forming a second high-temperature superconducting shield layer.
In the above-described methods of the present invention, the conductive pattern, conductive layer and conductive film can be obtained by forming a conductive paste layer on a surface of a ceramic substrate and subjecting the conductive paste layer to a heat treatment. Alternatively, they can be formed by plating a conductive material or vapor deposition of a conductive material.
It should be noted that the conductive pattern, conductive layer and conductive film should be of a type that contains silver as its main component.
As described above, with the method of manufacturing a superconducting quantum interference type magnetic fluxmeter according to the present invention, it is possible to form a coaxial type pickup coil on an outer surface of a cylindrical ceramic substrate so as to be integrated with an input coil, and therefore a high sensitivity can be achieved for a magnetic gradient in a vertical direction to the high-temperature superconducting quantum interference type element. Further, the scale of the pickup coil can be easily increased, and therefore the sensitivity can be easily improved.